The MPLS-OPS Archive

["M. ELK" <elkou141061@hotmail.com>]

Spice

Small story :

In 1990 , went to London  for training on certain IP BOX .
At that time the debate between distance-vector (RIP) and SPF (mainly at 
this time it was
OSPF , IS-IS was not in the picture) was not yet setlled down .

The training was outside LON so we hired a car to visit central London , 
with some
direction from the hotel we started the journey . and stopped for direction 
along the way .
we found that we are going in circle (loop)  , finally we reached .

Next trip , we got a map and followed the sign (road block ..etc ) and we 
reached central
London very smoothly .

at that time the above  case ,triggered an analogy in my mind between the 
above and RIP versus OSPF .

What was wrong with RIP ? simply we stopped for direction and take the 
suggestion
as faithvalue ie: we fully trusted the suggestion (we have no other choice) 
.  some
of those suggestion was bad and hence we got in a circle .


The book "rounting in the internet ,by Huitema" discussed the RIP behaviour 
in details ,
despite all the trick (poisoning ,reverse poisoing ,hold time ..etc ) still 
in certain topology
only the count to infinity could sort the pblm .

my guess that the pblm could be sorted out if the recieving node could judge 
if the advertisement recieved from neighbor is good or bad . this imply :
1) The advertisement packet carry info which could be checked for validity .
2) the recieving node have some algorithm to check those info and return
    "Good" or "Bad" .

the simplest sort of this info is the "path vector" , the recieving node 
could check
if any loop very easily .

but now it is no longer rip ,it is something like running eBGP (without 
policy , cost is the path count ie: the nbr of AS in the path . ) between 
all nodes and consider each node an AS .

As Eric indicated , RIP is dead/gone . The requirement of provider is now 
very high that even
fast convergence of IS-IS/OSPF (  1-2 sec) is not enough/adequate . The 
provider
requirement is now 50-100 msec . Their is many paper for msec convergence 
for SPF IGP
by decreasing the timer , eleminate to run full SPF ..etc ( Toward msec IGP 
convergence ,
draft-alaettingolu-isis-convergence-00  ,Nov 2000 ) .
The point is not just if RIP could be changed to eliminate possible loop 
creation but what is
the convergence time . If RIP could be changed to provide msec convergence 
,the provider's
will be ready to listen .

Brgds

_________________________________________________________________
Get a FREE online computer virus scan from McAfee when you click here. 
http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963

-------
The MPLS-OPS Mailing List
Subscribe/Unsubscribe:  http://www.mplsrc.com/mplsops.shtml
Archive: http://www.mplsrc.com/mpls-ops_archive.shtml